1. Technical Field
The disclosure relates to aircraft instruments.
2. Description of the Related Art
The “artificial horizon” (attitude indicator) was invented by Mr. Sperry and first flown by Jimmy Doolittle in 1929. It continues to be the primary flight instrument when the discernable horizon is not visible. It is also the primary instrument pilots depend upon to extricate themselves when a loss of situational awareness leads to spatial disorientation. All pilots, student pilots to professional and military pilots, are susceptible to spatial disorientation. Current aviation accident statistics indicate that prior art attitude indicator instrumentation continues to be insufficient to protect pilots from the hazards of spatial disorientation. Federal Aviation Agency statistics indicate that 15-17% of all aviation accidents, which includes commercial airlines, are the result of spatial disorientation and 90% of these accidents are fatal. Spatial disorientation is the military's number one cause of fatal accidents.
The leading cause of fatal aircraft accidents is Loss of Control in Flight (LOC-I). Boeing's 2009 Statistical Summary of Worldwide Commercial Jet Fleet Fatal Accidents—2000 through 2009, reports a total of 5001 fatalities. 22% of the accidents and 35% of the fatalities were attributed to LOC-I. As titled, this report includes only commercial jet aircraft and excludes non-jet commercial aircraft as well as general aviation and military LOC-I related accidents. In addition, examples of documented occurrences of LOC-I events that were successfully recovered typically go unreported. Therefore, in reality, the actual number of LOC-I incidences, is likely much greater.
LOC-I typically begins with a pilot's loss of awareness of the aircraft's bank attitude referred to as “Loss of Situational Awareness”. Situational Awareness is a comparison of an individual's perceptions of a situation to reality. Loss of situational awareness typically begins with an insidious slow banking, undetected by the pilot's inner ear. The pilot remains unaware that the aircraft is turning, believing that the aircraft is maintaining straight and level flight.
At some point, the pilot suddenly becomes aware that his perception of the aircraft's attitude is in disagreement with the aircraft's instrumentation. This realization of the conflict can quickly cause the onset of pilot spatial disorientation. Without proper and immediate recognition of the presence of spatial disorientation and the aircraft's real situation, and without immediate aircraft attitude corrective controls input, the aircraft can rapidly progress to an unrecoverable attitude.
Even the best of pilots will quickly become disoriented if they attempt to fly without instruments when there are no outside visual references. This is because vision provides the predominant sense we rely upon for spatial orientation. Therefore, spatial disorientation most commonly occurs when the horizon or other outside references are obscured, such as when clouds, haze, fog, snow or darkness are present. Loss of ability to determine position of the aircraft via the horizon can lead to disorientation and severe loss of flight control with potentially fatal results. The attitude indicator is the primary flight instrument for maintaining aircraft control in these conditions. Instrument flight training instructs pilots in coping with spatial disorientation. However, an instrument rating does not make a pilot immune to spatial disorientation and its potential for disaster.
Spatial Disorientations is categorized in three types:
TYPE I (Unrecognized): The pilot is oblivious to his disorientation, and controls the aircraft completely in accord with and in response to a false orientation percept. The pilot may believe he is flying level while actually in a banking dive, unaware of being within just seconds from a fatal crash. The pilot depends upon the attitude indicator to preclude the onset of Type I spatial disorientation. According to NATO, Report RTO-TR-HFM-118, pp 1.1, JUNE '07, “From the RAF and USAF SD (Spatial Disorientation) mishaps about 80% are Type I, i.e. unrecognized spatial disorientation.”
Statistics indicate that prior art has not effectively addressed or arrested Type I spatial disorientation.
TYPE II (Recognized): The pilot may experience a conflict between what he feels the aircraft is doing and what flight instruments show. Such confusion can cause a pilot to delay corrective action or initiate incorrect controls input, exacerbating the already dangerous situation. Again, the attitude indicator is the primary flight instrument for determining and verifying the attitude of the aircraft. Difficulty in interpreting the attitude of the aircraft jeopardizes the ability to initiate a recovery. Statistics indicate that prior art attitude indicators lend themselves to confusion and misinterpretation during occurrences of Type II spatial disorientation. According to NATO, Report RTO-TR-HFM-118, pp 1.2 JUNE '07, “20% of the SD mishaps involve recognized SD (Type II), where pilots know they are disoriented, but cannot equate the conflict between instrument readings and perceived motion and/or attitude.”
TYPE III (Incapacitating): The pilot experiences the most extreme form of disorientation stress. The pilot may be aware of the disorientation, but unsuccessful attempts to determine the aircraft's attitude leaves the pilot mentally and physically overwhelmed to the point he is unable to successfully recover from the situation. He may freeze at the controls, or make control inputs that tend to exacerbate the situation rather than affect recovery. The inability to quickly and properly interpret the attitude indicator display can cause a pilot to succumb to Type III spatial disorientation.
Three Critical Steps for successfully combating the perils of spatial disorientation:
Critical Step 1: The pilot must recognize, in advance, conditions that may lead to loss of situational awareness and spatial disorientation.
Critical Step 2: The pilot must properly interpret the aircraft's instrumentation to determine aircraft attitude in order to initiate appropriate corrective action.
Critical Recovery Step 3: The pilot must apply aircraft controls correctly to affect a recovery.
Prior art attitude indicators do not provide pilot assistance relative to Critical Step 1. In particular, prior art attitude indicators tend to exhibit inherent ergonomic design flaws that may compromise a pilot's ability to comply with Critical Step 2. Without certain ability to properly comply with Critical Steps 1 and 2, the ability to perform Critical Step 3 is left in the hands of the divine.
Through numerous generations of development, many of the operational design deficiencies of the prior art have been addressed. Notably, the advent of solid state technology with solid state accelerometers and gyroscopes have adequately addressed many of the limitations of vacuum and electric/mechanical gyroscopes, such as gimble lock, which manifests itself as a tumbling attitude indicator at steep banks, nose high and nose low attitudes. However, the ergonomic deficiencies of the original design have not been successfully addressed. These deficiencies tend to manifest themselves in pilot confusion and often misinterpreted referencing of unanticipated pitch and bank attitudes.
It is generally understood that the tendency to misinterpret bank angle presentations increases as the aircraft's attitude departs further and further from wings level flight and level pitch. Therefore, upon the encroachment of an unanticipated attitude, at the time when dependency on the pilot's proper interpretation of the aircraft's attitude is most critical, when rapid and accurate aircraft controls input are paramount to execute a proper recovery, current attitude indicator presentations tend to further confuse and disorient pilots.
The uncertainty of consistently being able to accurately interpret an aircraft's attitude, such as during a loss of situational awareness and impending spatial disorientation event, can confuse and even mentally and physically paralyze a pilot as in Type III Spatial Disorientation. Contributing to the possibility of Type III Spatial Disorientation is the unsettling sight of watching the attitude indicator spin or tumble in steep pitch and/or bank attitudes, making it virtually impossible to determine the precise attitude of the aircraft and what corrective action is required to recover to level flight.
Much of the confusion related to the prior art has been introduced in attempts to overcome past ergonomic deficiencies. Over time, two attitude indicator presentations have evolved in attempts to mitigate attitude indicator misinterpretation. Unfortunately, these attempts have resulted in potentially dangerous and conflicting inconsistencies between how each represents the horizon and its correlation to bank angles, bank pointer, pitch angle and aircraft symbol.
(Prior Art FIG. 1). This design, referred to as “Outside-In” or “Moving Plane—MP” embodies an artificial horizon line midway between the top and bottom of the instrument face. The horizon line and bank scale are fixed in position. The bank pointer moves in concert with aircraft banking. When the aircraft banks 20-degrees right, the bank scale remains fixed while the bank pointer rotates to the 20-degrees right bank scale index. The bank pointer represents both direction and magnitude of bank.
(Prior Art FIG. 2). The alternative presentation, referred to as “Inside-Out” or “Moving Horizon—MH” embodies an artificial horizon line midway between the top and bottom of the instrument face that responds to aircraft bank. The bank pointer moves in concert with the horizon. The bank scale is fixed in position and the aircraft symbol is fixed in the wings level position. When the aircraft banks 20-degrees right, the bank pointer rotates left positioning the bank pointer to the 20-degree left bank scale index. The bank pointer represents magnitude of bank correctly, but displays the bank in the direction opposite of the actual aircraft bank attitude.
These two attitude indicator presentations place the “bank pointers” in direct conflict with each other as to the direction the aircraft is banking. The potential for pilot confusion is obvious. Such confusion can be catastrophic. Many pilots admit to misinterpreting (and numerous studies confirm that pilots often misinterpret) banking attitudes as presented on prior art attitude indicators, resulting in control inputs in a direction opposite that required to correct the bank, exacerbating the situation. The technique adopted by many pilots is to “jiggle” the ailerons control in the perceived-to-be-correct direction while monitoring the resulting attitude change. If the aircraft responds in the desired direction, the pilot continues with that particular control input. If, however, the attitude moves in the direction opposite of that desired, the pilot reverses control input. Valuable recovery time is lost attempting to ascertain aircraft attitude and appropriate control inputs when using such a technique.
Confusion created by conflicting designs is magnified when:                The pilot is not instrument rated but finds himself in meteorological conditions requiring transition to the attitude indicator to maintain aircraft control.        The pilot is instrument rated but no longer proficient and finds himself in meteorological conditions requiring transition to the attitude indicator to maintain aircraft control.        The pilot is relatively new to a specific aircraft and has not had sufficient time to become proficient with the type of attitude indicator installed, (MP or MH).        The pilot flies several aircraft that may have either or both types of attitude indicators installed. A particular aircraft has one type attitude indicator as the primary and the other type as the backup attitude indicator.        The pilot is attempting to recover from a spatial disorientation event.        Anytime the pilot is in a stressful situation that requires the use of the attitude indicator to ensure safety of flight.        
Prior art FIGS. 3 and 4 are both of an aircraft in a 20-degree nose down, 130-degree right bank. These figures provide vivid illustrations of the differences between the presentations of present day, prior art attitude indicators, with FIG. 3 using an MP-type indicator, and FIG. 4 using an MH-type indicator. Notably, these indicators provide significantly different images that can cause the pilot obvious confusion; delaying or precluding a pilot's corrective action to bank and pitch excursions. To compensate for these deficiencies and ensure proper interpretation of and response to present state of the art attitude indicator presentations, the pilot oftentimes indulges in numerous cockpit instrument comparative observations, analysis and conclusions before initiating action. When relying on the prior art attitude indicator for aircraft control, five Time-Critical questions typically are answered by deciphering the attitude indicator presentation:                1. Is the aircraft banked left or right?        2. Is the aircraft pitched up or down?        3. Is the aircraft upright or inverted?        4. What are the appropriate aircraft control inputs to initiate the proper correction?        5. Are the initial conclusions and resulting actions correct?        
More recent attempts to resolve ergonomic deficiencies have been limited to incorporating color into traditional presentations on modernized displays of Electronic Flight Instrument Systems (EFIS). Beautification of old technology presentations has failed to make the attitude indicator more intuitive or a safer flight instrument. Arguably, the increased amount of data displayed on EFIS's, concurrent with the prior art attitude indicator display, can further compromise the pilot's ability to effectively interpret displayed information, particularly in adverse attitudes.
The ergonomic problems that compromise flight safety (and that are often the contributory cause of aircraft accidents) reside with the traditional presentation of aircraft attitude relative to the horizon. All prior art designs are anchored to the concept of presenting the artificial horizon as the basis of aircraft attitude reference. Attempts to simultaneously overlay pitch, bank and aircraft symbology on an artificial horizon (all of which are in an unstable state), have proven to be ineffective. Prior attempts to replicate a pilot's eye view of the horizon on an attitude instrument face have proven to generate confusion and aircraft attitude misinterpretation. Confusion occurs because prior art attitude indicators present the pilot with gyrating visual information that conflict with pilot sensations, as during spatial disorientation events. For instance, the pitch scale moves up and down, and rotates with bank changes, all in relation to an artificial horizon line that may also be moving. Depending on the particular prior art design, the bank pointer and aircraft symbol may be in a continuous state of movement as well. The very instrument that is supposed to provide clarity concerning aircraft attitude, due to inherent ergonomic deficiencies, actually promotes confusion, misinterpretation and perilous loss of aircraft control.
Present dogma is that the only defense against erroneous readings of aircraft attitude from an artificial horizon display (Prior Art) is better training. The aforementioned statistics tend to indicate that this strategy has failed.